Concentric drain plug.

[chrisx1]

I noticed that my carb was leaking from the drain plug. Does anyone use a rubber O ring instead of or with the fibre washer ? Also not sure if the O ring would be rotted by the fuel.

[iansoady]

A Viton one would be OK although in theory that's not the best place for an O ring. Fibre washers these days seem to be very hard. An alternative is a thin smear of Wellseal either side of the fibre washer.

[chrisx1]

A Viton one would be OK although in theory that's not the best place for an O ring. Fibre washers these days seem to be very hard. An alternative is a thin smear of Wellseal either side of the fibre washer.

The washers I have are very thin and as you say quite hard. I may give the well seal a try with two washers.

[limeyrob]

Plastic or brass plug?  I find the plastic distort over time.

[V500]

The washers I have are very thin and as you say quite hard. I may give the well seal a try with two washers.

Shouldn't be necessary. Just make sure you soak the washers in petrol or oil overnight to soften them sufficiently. O rings sound like a bad idea.

[DMadigan]

Viton O-rings are fuel resistant. You need a drain plug with a face groove for the O-ring to keep it from squashing out.

[JJC]

Rubber isn't a good idea.  You won't be able to tighten the drain plug without squishing out the rubber.  The real problem is that it's not a very good design.  The sealing face of the float bowl is very thin and the drain plugs seem to have an undercut on the thread such that the washer doesn't sit centrally.  After 40 plus years I am still searching for a good system that doesn't leak or come lose.  I tried some plumbers pipe thread seal.  It sealed great but turned out to be a very bad idea as the drainplugs were in solid when I tried removal at a later date.

[DAVE BRADY]

Hi,

An interesting story re conc. drain plug.
Back in 2001 we were lucky enough to go the BSAOC Inter. in Australia.
A requirement for shipping the bikes was no fuel in the tank.  So to pre-empt the corks in the fuel taps drying out some grease was applied.  This worked so no leaky taps or need to replace the corks. 
First day riding and heading for the Great Ocean road my bike starts to run rough as if running out of fuel.  Strange as we had not long filled up but on went the reserve with no affect.  Upon stopping there was reek of fuel and it was running out of the bottom of the carb.
So taps off to keep what was left.
The drain plug had come undone and had dropped out.  Disaster. In the middle of nowhere there was no choice but to start walking back to try to find it.  After few steps, I thought that if fate was on my side it may have dropped on to part of the frame.  On looking, I saw that it was sitting on the top of the filter that is fitted to my A65. So replaced and secure onward but with the nagging thought of how much petrol had I lost and how far was it to the next petrol station.  Luckily My wife's '51 Flash has a bit more capacity so I could nick some of her fuel.
Twice I had to beg for 1/2L until ahead, at a cross roads stood a petrol station and salvation.
My theory is that due to the heat in the container the fibre washer had dried out allowing the plug to loosen and eventually drop out.
As a last resort I was going to whittle a plug out of a piece of eucalyptus.

Dave.

[JJC]

Same thing happened to me once also.  These days I carry a spare and also keep an eye on the tightness.  They have a habit of coming undone.

[limeyrob]

There are Concentric float bowls around with no drain plug. Perhaps fit one of them?  I doubt they are especially sought after.

[V500]

Those float bowls were fitted to very early Concs. The drain plugs are more useful to do jet changes by the side of the road.

[DMadigan]

You can get delrin washers to replace the fibre.
If the plug has a face groove for the O-ring it will not squash out.
Drainless bowls are likely rare as they are used by triples converted to electric start to make clearance with the starter motor.

[nablats]

Just a thought, (I have a spare float bowl), why not forget about the washer and use JB weld to permanently stop the drain plug falling out?

[limeyrob]

The brass plugs don't leak, I think the problem the nylon does not hold its shape.  I suspect this could be made worse by ethanol in petrol.
There is a guy on e-bay who sells Concentric float bowl with the drain hole plugged, looks a neat job, I think its for triples.

[DAVE BRADY]

Hi,

This plug is quite useful. Sometimes a bit of 'stuff' can gather there with the potential of blocking the main jet, any water that gets in the fuel will accumulate there, if a quick jet change is needed it can easily be done as it means not needing to remove the float bowl.
My story re plug falling out was exceptional rather than common but a bit of PTFE tape can also help to keep it in place.

Dave.